first: reset your pc, sometimes its very helpful

maybe some memory buffer is overloading if you too long use your pc and some programs
second: check temperatures inside pc via BIOS or programs like Everest, Aida etc, maybe processor or north bridge is overheating - we have summer

third: if something like above is too hot try to clear dust inside (radiators, fans etc.)
also defragment your hdd, try to close all of unused programs, never use 2x anti-virus progs at the same time etc
greetings